Zsolt Illyefalvi-Vitez

Low temperature soldering on biopolymer (PLA) Printed Wiring Board substrate

The applicability of decomposable biopolymer (polylactide - PLA) as Printed Wiring Board (PWB) substrate was investigated. A novel approach for low temperature reflow soldering was applied. Different types of PLA boards were prepared and each type was qualitatively characterized. The realized circuit was designed for the use of Surface Mounted (SM) components. The low maximum process temperature of PLA boards was a key aspect to set soldering temperatures. 58Bi42Sn solder alloy was chosen to match the lower soldering temperature range required by the PLA board material. Steps of reflow soldering technology (stencil printing, component placement, reflow soldering) were applied using 0603 discrete components and were inspected during the circuit assembling process. Hot soldering iron, IR radiation, hot gas method and Vapour Phase Soldering (VPS) were applied for heat transfer during the experiments. VPS was found the best for heat transfer to melt the low temperature (138 °C) solder alloy. The results verified the flexibility and usability of the VPS in the field of special applications. The quality of boards was examined with cross-section optical inspection; the solder joints were evaluated with shear force tests. Typical failures were also analyzed.

Virtual laboratory support for microelectronics packaging education

The development of information technology has opened new perspectives in electronics packaging education to prepare engineers for the needs of the 21st century. A project for the creation of virtual laboratory environment in the field of microelectronics packaging is proposed and outlined in this paper. Educational courses for undergraduate students and working engineers can use the proposed virtual laboratories through the internet in order to support their training and extend their skills into emerging fields.

Characterization of vapour phase soldering process zone with pressure measurements

Purpose – The purpose of this paper is to present a novel approach on the process zone characterization for direct feedback regarding the state of vapour, in order to assure a better monitoring, control and understanding of the process.Design/methodology/approach – Different pressure sensors were applied in an experimental vapour phase soldering (VPS) station, where the hardware setup was dedicated to the current experiments. Static and dynamic pressure values were analyzed and correlated with additional thermal measurements.Findings – The results reveal the dynamics of the vapour blanket generation. The correlated measurements show different stages of the process initialization, highlighting better accuracy than sole temperature measurements of saturated vapour identification. It is possible to trace the height of the available saturated vapour blanket with static pressure measurements.Practical implications – The VPS process may benefit from the more precise saturation detection, giving better control o...

Package–on–Package – Review on a Promising Packaging Technology

Package-on-Package (PoP) components are BGA packages stacked on each other. With this method not only board space is saved, but signal routes are also shortened. It was presented by a cooperation of Amkor and Nokia [1]. The vertical 3 dimensional stacking of BGA components broadens the possibilities of planar surface mounting technology. The PoP technology is constantly evolving; the latest solutions offer wide variety of bumping and stacking technologies. This paper is a review on this aspiring 3D packaging method. Preliminary soldering experiments with dummy packages are also presented.

Recent advancements in MCM-L imaging and via generation by laser direct writing

The paper presents some preliminary results and describes the state of a research project that aims at the improvement of the quality of MCM-L circuit boards by the application of UV lasers for the following processes. 1) Pattern generation by direct writing using Nd:YAG (IR, visible or UV) laser. The copper clad laminate is covered by some protective layer, and the pattern is directly written to this layer by material removal (ablation). The pattern of the copper layer is prepared either by wet chemical etching or applying the electroplating-stripping-etching process sequence. 2) Photo-mask exposure by direct writing. In this case a photoresist protective layer is exposed by a UV He-Cd laser, and after developing it is used for the conventional image transfer process. 3) Through board via generation by contour direct writing using frequency multiplied Nd:YAG laser. It means that holes are drilled by moving the well-focused laser beam along their contour. 4) Blind via generation by controlled number of pulses using the same frequency multiplied Nd:YAG laser. In this case the whole area of the via is exposed, and the hole is deepened shot by shot.

Soldering profile optimization for vapour phase reflow technology

Vapour Phase Soldering (VPS) is an alternative method for widespread reflow soldering technologies (e.g. infrared or convection type). VPS has emerged in the last few years after the introduction of Galden fluid. The vapour of Galden is used as the heat transfer medium. The main advantages of VPS are the lower peak temperature, nitrogen/oxygen-free inert atmosphere, the improvement in solder wetting and the reduction of the profiling time [1]. One disadvantage of VPS is the non-controllable, linear soldering profile achieved by common VPS soldering method [2]. With controlled dipping of solder goods into the vapour space, non-linear soldering profiles can be obtained. This method is called Soft-VPS (S-VPS) and was developed and patented by IBL. With this method, custom temperature gradients and profiles can be realized, reducing voids, tombstoning and avoiding high thermal stress on the boards [3]. This paper presents thermal profiling of an experimental VPS station from the aspect of this method, with a successful optimization of the process. The optimized profiles for low melting point (138 °C) lead-free Sn-Bi solder paste were inspected. Soldering results of 0603 chip size resistors were then evaluated with resistance measurements and x-ray inspection.

Analysis of vapor phase soldering in comparison with conventional soldering technologies

Vapor phase soldering (VPS) has been investigated to improve the knowledge about the vapor generation, progression and condensation processes. Measuring methods for the investigations have been developed and applied. In an experimental VPS system the following parameters have been studied during the heating up and cooling down processes: the temperature distribution in the chamber by measurements using Pt thermistors of ladder arrangement; the temperature distribution in and the heating efficiency of the vapor blanket as function of height by varying the vertical position of the sample with temperature sensors on it; the height of the vapor blanket by a special fiber optic probe; the height of the vapor blanket by applying a floating polymer pillow as vapor level indicator; and the status of the vapor/mist/rain phases by optical inspection of light scattering. The experimental investigations show that high proportion of the vapor condensates in the space on the level of the cooling tube in the upper part of the chamber, therefore the vapor is rather in mist phase full with falling droplets of the condensed fluid, which has a determining effect on the heating efficiency of the medium.

Testing the Impact of Pb-free Soldering on Reliability

The electronics industry is in the transition to lead-free technology, and it is very important for all industrial performers, to keep pace with this process. In order to produce the electronics module of required quality and reliability, the application of lead-free soldering alloys requires new design, materials, processing, inspection and rework considerations. It is also a new challenge to test and predict the reliability and the life-time of the lead-free solder joints fabricated with new materials combinations and process parameters. In the paper, the general requirements of solder joints, the theoretical considerations of the applicability of combined accelerated life-time test methods and the results of some experimental work regarding lead-free solder joints are discussed

Effect of patterned copper layer on selective polymer removal by 355 nm laser

Ab s t r a e t Optimization of lascr parameters is a challenge in case of microvia drilling. It is even more complicated to find the right parameters for large area scanning, where not only pulse energy and burst play important roles but also pulse repetition rate, scanning speed and overlap. In case of selective material removal the above process parameters define the amount of the ablated material (etch depth) and the processing time. This paper dcscribes results of experiments carried out to find correlation between the process parameters and the quantity of the ablated material. Flexible polyimide substrates of different thicknesses were processed by frequency trippled, Q-switched Nd:YAG laser. The samples were examined by surface profiler and their cross-sections by optical microscope. The experiments showed that the amount of the ablated polymer is influenced by the features of the patterned copper layer. Even though there is no direct interaction between the laser beam and the copper layer, the thermal conductivity of the circuit pattcm influences the temperature of the processed polymer. Because of this phenomenon there is a need to control the laser processing parameters according to the circuit pattern. The correlations we have found between the process parameten and thc etch depth make this controlled laser material removal possible.

Distance learning - how to use this new didactic method in education of electronics engineering?

Distance learning (DL) is an instructional delivery system that connects learners with educational resources. In microelectronics and microsystems interconnection and packaging technology, the preparation of electronics engineers for the ever growing requirements is especially a challenge for todays education, and there is an essential need for the application of advanced curricula and teaching methods. In the present paper, the driving forces for the development of curricula and didactic methods are outlined, followed by the detailed discussion of the needs for and the applicability of distance learning. Then, an example is provided for the application of the Internet-based performance centered instructions (IPCI) model for providing Web-based DL experiments in the special field of surface mounting technology (SMT) for students of electrical engineering and graduate engineers interested in microelectronics packaging and interconnection technology. Finally conclusions are drawn and further efforts are outlined.